Stock material or miscellaneous articles – Circular sheet or circular blank – Recording medium or carrier
Reexamination Certificate
2001-11-13
2004-02-03
Resan, Stevan A. (Department: 1773)
Stock material or miscellaneous articles
Circular sheet or circular blank
Recording medium or carrier
C428S421000, C428S336000, C428S690000, C428S690000, C427S130000, C427S131000, C427S553000
Reexamination Certificate
active
06686019
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an improved method for stabilizing a thin film of a composite lubricant material applied to the surface of a thin film recording medium, particularly for reducing static and dynamic frictional coefficients thereof when utilized in combination with a flying head read/write transducer, and to improved thin film recording media obtained thereby. The invention finds particular utility in the manufacture and use of thin film type magnetic or magneto-optical (“MO”) data/information storage and retrieval media comprising a layer stack or laminate of a plurality of thin film layers formed on a suitable substrate, e.g., a disk-shaped substrate, wherein a thin topcoat layer comprised of a composite lubricant material is applied to the upper surface of the layer stack or laminate for improving tribological performance of the media when utilized with read/write transducer heads operating at very low flying heights.
BACKGROUND OF THE INVENTION
Magnetic and MO media are widely employed in various applications, particularly in the computer industry for data/information storage and retrieval purposes. A magnetic medium in, e.g., disc form, such as utilized in computer-related applications, comprises a non-magnetic disk-shaped substrate, e.g., of glass, ceramic, glass-ceramic composite, polymer, metal, or metal alloy, typically an aluminum (Al)-based alloy such as aluminum-magnesium (Al—Mg), having at least one major surface on which a layer stack or laminate comprising a plurality of thin film layers constituting the medium are sequentially deposited. Such layers may include, in sequence from the substrate deposition surface, a plating layer, e.g., of amorphous nickel-phosphorus (Ni—P), a polycrystalline underlayer, typically of chromium (Cr) or a Cr-based alloy such as chromium-vanadium (Cr—V), a magnetic layer, e.g., of a cobalt (Co)-based alloy, and a protective overcoat layer, typically of a carbon (C)-based material, e.g., diamond-like carbon (“DLC”) having good tribological properties. A similar situation exists with MO media, wherein a layer stack or laminate is formed on a substrate deposition surface, which layer stack or laminate typically comprises a reflective layer, e.g., of a metal or metal alloy, one or more rare-earth thermo-magnetic (RE-TM) alloy layers, one or more transparent dielectric layers, and a protective overcoat layer, e.g., a DLC layer, for functioning as reflective, transparent, writing, writing assist, and read-out layers, etc.
Thin film magnetic and MO media in disk form, such as described supra, are typically lubricated with a thin topcoat film or layer comprised of a polymeric lubricant, e.g., a perfluoropolyether, to reduce wear of the disc when utilized with data/information recording and read-out transducer heads operating at low flying heights, as in a hard disk system functioning in a contact start-stop (“CSS”) mode. Conventionally, the thin film of lubricant is applied to the disc surface(s) during manufacture by dipping into a bath containing a small amount of lubricant, e.g., less than about 1% by weight of a fluorine-containing polymer, dissolved in a suitable solvent, typically a perfluorocarbon, fluorohydrocarbon, or hydrofluoroether.
The lubricity properties of disk-shaped recording media are generally measured and characterized in terms of dynamic and/or static coefficients of friction. The former type, i.e., dynamic friction coefficient, is typically measured utilizing a standard drag test in which the drag produced by contact of a read/write transducer head with a disk surface is determined at a constant spin rate, e.g., 1 rpm. The latter type, i.e., static coefficients of friction (also known as “stiction” values), are typically measured utilizing a standard contact start/stop (“CSS”) test in which the peak level of friction is measured as the disk starts rotating from zero (0) rpm to a selected revolution rate, e.g., 5,000 rpm. After the peak friction has been measured, the disk is brought to rest, and the start/stop process is repeated for a selected number of start/stop cycles. An important property of a disk which is required for good long-term disk and drive performance is that the disk retain a relatively low coefficient of friction after many start/stop cycles or contacts with the read/write transducer head, e.g., 20,000 start/stop cycles.
The most commonly employed lubricants utilized with thin film, disk-shaped magnetic and MO media, i.e., perfluoropolyether (“PFPE”)-based lubricants, perform well under ambient conditions but not under conditions of higher temperature and high or low humidity. Studies, as described in, for example U.S. Pat. No. 5,587,217, the entire disclosure of which is incorporated herein by reference, have indicated that the tribological properties, and perhaps corrosion resistance, of perfluoropolyether-based lubricants utilized in the manufacture of thin film recording media can be substantially improved by addition thereto of an appropriate amount of a cyclotriphosphazene-based lubricant additive, e.g., a polyphenoxy cyclotriphosphazene comprising substituted or unsubstituted phenoxy groups, to form what is termed a “composite lubricant”.
Currently, bis (4-fluorophenoxy)—tetrakis (3-trifluoromethyl phenoxy) cyclotriphospazene (available as X-1P™ from Dow Chemical Co., Midland, Mich.) is the lubricant most commonly with perfluoropolyether-based lubricants for forming composite lubricants for use with thin film magnetic and MO media. However, as disclosed in U.S. Pat. Nos. 5,718,942 and 5,908,817, the disclosures of which are incorporated herein by reference, the use of X-1P as a lubricant additive for forming composite lubricants comprising commonly employed perfluoropolyether-based lubricants in the data storage industry (e.g., Fomblin Z-DOL™ and Fomblin Z-TETRAOL™, each available from Ausimont, Thorofare, N.J.) incurs a disadvantage in that the former (i.e., the cyclotriphasphazene-based lubricant additive) has very low solubility in the latter (i.e., the PFPE-based primary lubricant).
For example, X-1P, in combination with Z-DOL at levels up to about 5 wt. %, reduces stiction and increases the stability of Z-DOL. However, because X-1P is virtually immiscible in PFPE-based lubricants, phase separation typically occurs at the optimal X-1P/PFPE ratios. The phase separation leads to chemical non-uniformity of the lubricant film on the media (e.g., disk) surface, as by the so-called “balling” effect, which tends to affect the tribology (i.e., durability) of the head/disk interface, particularly when the thickness of the X-1P exceeds about 1-2 Å. As a consequence of the poor compatibility of the X1P lubricant additive with the Z-DOL or Z-TETRAOL primary lubricant, the maximum amount of X1P that can used therewith is severely limited, typically to about 10% of the total lubricant thickness. Moreover, X-1P/PFPE mixtures do not exhibit performance enhancement over PFPE alone when the X-1P layer thickness is less than about 1Å, or at X-1P concentrations less than about 1 wt. %. Thus, according to current practice, the effective concentration window for use of X-1P in combination with PFPE is quite narrow, and special process control is required to achieve optimal performance. Notwithstanding such special process control, phase separation of the X-1P additive, accelerated lubricant loss, and a large amount of transducer head smear frequently occur even with such low additive contents.
U.S. Pat. No. 6,099,762, the entire disclosure of which is incorporated herein by reference, discloses a process for enhancing the bonding, thus durability, of thin lubricant layers comprised of a PFPE, a phosphazene, or both, to media surfaces by means of a process comprising exposing the lubricant layer or film to infra-red (“IR”) and ultra-violet (“UV”) radiation, either simultaneously or sequentially, wherein the IR radiation effects heating of the lubricant layer or film to a temperature above about 150° F. but less than about 500° F., and the UV radiation comprises a
Liu Jianwei
Stirniman Michael Joseph
McDermott & Will & Emery
Resan Stevan A.
Seagate Technology LLC
LandOfFree
In-situ stabilization of composite lubricant/additive films... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with In-situ stabilization of composite lubricant/additive films..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and In-situ stabilization of composite lubricant/additive films... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3355298